1. Field of the Invention
The present invention is directed to polymeric materials made of biodegradable, bioabsorbable triblock copolymers and implantable devices (e.g., drug-delivery stents) containing such polymeric materials.
2. Description of the State of the Art
Angioplasty is a well-known procedure for treating heart disease. A problem associated with angioplasty includes formation of intimal flaps or torn arterial linings which can collapse and occlude the conduit after the balloon is deflated. Moreover, thrombosis and restenosis of the artery may develop over several months after angioplasty, which may require another angioplasty procedure or a surgical by-pass operation. “Stenosis” refers to a narrowing or constriction of the diameter of a bodily passage or orifice, and “restenosis” refers to the reoccurrence of stenosis in a blood vessel or heart valve after it has been treated (as by balloon angioplasty, stenting, or valvuloplasty) with apparent success.
Stents are often used in the treatment of atherosclerotic stenoses in blood vessels. To reduce the partial or total occlusion of the artery by the collapse of arterial lining and to reduce the chance of thrombosis and restenosis following angioplasty in the vascular system, a stent may be implanted in the lumen to reinforce body vessels and maintain the vascular patency. A “lumen” refers to a cavity of a tubular organ such as a blood vessel. As a mechanical intervention, stents act as scaffoldings, functioning to physically hold open and, if desired, to expand the wall of a passageway, e.g., a blood vessel, urinary tract or bile duct.
Stents are also used as a vehicle for providing biological therapy. Biological therapy can be achieved by medicating the stents. Medicated stents provide for the local administration of a therapeutic substance at the diseased site, thereby possibly avoiding side effects associated with systemic administration of such medication. One method of medicating stents involves the use of a polymeric carrier coated onto the surface of a stent, in which a therapeutic substance is impregnated in polymer.
Late stent thrombosis has emerged as a concern for drug-delivery stents. The incidence of late stent thrombosis appears to be higher with drug-delivery stents than with the corresponding bare metal stents. One potential cause of late thrombosis with drug-delivery stents is a chronic inflammatory or hypersensitivity response to the polymeric coating on the stent.
The present invention addresses late stent thrombosis and offers other advantageous features.